Multiplex telephony and telegraphy.



G. O. SQUIBR. MULTIPLEX TZLEPHON I AKD TELEGRAPHY.

APPLIGATIOH FILED $53, 5, 1910.

980,856, Patented JalL 3,1911.

A Fyl I 'ashi' HELTEE .STATES FATE T @FFXCE.

GEZQRGE OWEN SQUIER, OF THE UNITED STATES ARMY.

MULTIPLE}! TELE1HONY AND TELEGRAIHY.

Application filed November 5, mo.

Specification of Letters Patent.

Iatcnted Jan, 3, 1911.

Serial No. 590,801..

(DEDICATED TO THE PUBLIC.)

1' I r115 '12?! am it may concern:

ilovernment of the U12 ited States or any of its oiiicers or employees in the prosecution of work for the United States or by any per- .son in the United States without the payment of any royalty thereon.

This invention relates to multiplex telephony and telegraphy and has as its object the simultaneous transmission of a plurality of telephonic and telegraphic messages over a single telephonic circuit A further object of the invention is the disposition of the variouselemcnts in such a manner to eliminate all cro' talk or other harmful effects of one message upon another.

A further objoct is to impress electric waves or oscillations of such different frequencies upon the circuitas to make possible the selection and complete independence of the various messages.

i-i further object is to supcrimpose upon a standard battery telephone circuit, as now commercially used, one or more additional telephonic and telegraphic circuits without any. interference of the various messages.

In accomplishing the above results use is made of electromagnetic waves or oscillations of high frequency guided by wires.

In the whole range of electromagnetic waves, which may be looked upon as a spectrum extending from the ultra-violet rays on' the one hand to the exceedingly slow oscillations. such as are used on long submarine cables, on the other hand, use has been made of all parts for various purposes with the exception of two well defined inervals. one extending from a frequency of about 3x10 of the extreme infra-red, to x10. which are the shortest electromagnetic waves yet produced by electrical apparatus and another interval extending from about 100,000 cycles per second to about 15,000 to 20.000 cycles per second. This latter range of frequencies represents a ractically unexplored field which I have ound by experiment to be very useful in solving the problems of multiple telephony and telegraphyupon wire circuits.

\Vhen reference is made in this application to high frequency waves or oscillations, it is understood to mean oscillations with a frequency above human audition, or ultrasound frequencies.

1 he limit of audibility being a physiological function is well known to vary considerably, but it is in the neighborhood of 15,000

to 20,000 cycles per second.

By employing ultra-sound electromagnetic wave frequencies as the vehicle for transmitting telephonic and telegraphic messages, it is evident that all harmful ctiects to any element of the battery telephone apparatus are immediately removed, since not only are any such -eli'ects very minute, in character, by virtue of the high period of the oscillations, but also, even if there were anyetfects in the telephone receiver, or transmitter, or any other part of the apparatus, it could not be detected by a human being, since the natural limitations of the ear afford a mosteii'ective and sure separation between all frequencies above 15,000 to 20,000 per second on the one hand, and all frequencies below 15,000 to 20.000 and down to about per second, which is the lower limit of audibility. Therefore, a fundamental principle of this system may he said to be, from one viewpoint, the utilization of this unalterable characteristic of the human car.

With such frequencies as are used in ordi nary battery telephony the so-called phenomenon of skin effect is comparatively small, and the currentis fairly well distrib uted throughout the cross-section of the conductor. As the frequency increases the skin effect becomes more pronounced and the energy appears to be more and more transmitted or stored in the ether surrounding the conductor. For this reason the battery telephone current is largely a conduction current through metal, and the ohmic resistance of the wire is one of the principal elements which limits long distance telephony at present, whereas in commercial wireless telegraphy. in which frequencies from 100,000 up to several millions are used,

the impressed energy is chiefly radiated into the ether.

In the intermediaterange from say 20,000 to 100,000 and above the energy is largely carried by the ether, but, is still suliiciently linked to the' conductor to prevent excessive radiation into the ether. The conductor while carrying but a small part of the energy at its surface nevertheless acts as an efiicient guide for the high frequency electromagnetic waves. In accordance with these principles, use is made of these ellicient-ly guided electromagnetic ether waves as a vehicle to carry the telephonic or telegraphic message.

In accomplishing the above it has been found necessary and 'suificient to combine the engineering practice of wireless telegraphy and telephony with the engineering practice of wire. telegraphy and telephony Since wireless engineering deals with frequencies much higher than ordinary telephony it is obvious that dilferent dimensions for capacities and inductances must be used, for instance, whereas the ordinary tele phonic practice makes use of condensers with capacity of several microfarads it is here necessary to use capacities of the order of magnitude of thousandths of a microfarad and inductances of millihenries.

The present invention makes use of the types of apparatus, engineering methods, etc., now practiced in the wireless art and applies them to the transmission of electromagnetic waves along wires, with the result of an enormous increase in elliciency of such transmission over the ordinary method employing antennae at transmitting and receiving stations. The circuits employed in this invention are ordinary telephonic circuits, such as now used in Wire telephony and telegraphy, and are very poor radiators of electromagnetic energy; in fact, the regular twisted-pair paper-insulated lead-covered telephonic cable affords a circuit for such electromagnetic waves which produce a very closely bounded system and the energy is principally conveyed in such a circuit in the minute layer of ether separating the two metallic conductors. In this manner, and by these means, a most efiicien system of directive high frequency telegraphy and telephony is attained, and also any interferences between neighboring circuits operated by this sys em is eliminated, so that a plurality of such circuits may be brought to the same switchboard with no harmful interfering efiects.

It is old in the art.- to use high frequency oscillations and modify these in accordance with speech vibrations by eflecting some electromagnetic constant or constants of the circuit in which the oscillations take place.

It is possible to change the capacity, the inductanoe or the resistance of such a circuit or combinations of these, and while 'I do not wish to limit myself to any one of.thcsc.

and telephony, being satisfactory so long as it is a quantitative or integrating detector. By means of suitable translating means the oscillations are then transformed into telephonic currents, all of which is described more in detail hereafter.

Since a plurality of high frequency waves of different frequencies may be impressed on the same line, and since these may be selectively separated from each other by suitably tunedcircuits, it is obvious that multiplex telephony may be accomplished. Also, for the reasons stated above, it has been found that these high frequency ,waves may exist on the same line with ordinary battery telephone currents without in any way affecting them, and thus this system of multiplex telephony may be applied to the usual telephonic circuits without the presence of harmful effects, such as cross-talk or other disturbances.

It has been found necessary, in order to obtain efiicient results, to make use of such detectors as are commonly found in the wireless telegraphic art. Attempts have been made at multiplex telephony, but I have found these inoperative, for the reason, among others, that no detector or equivalent device has been used. These detectors are not used because of any greater sensitiveness to electrical energy than resides in the telephone receiver itself, but because the energy, being in the form of rapid oscillations, cannot affect the telephone or other indicating device. These rapid oscillations cannot sensibiy affect the telephone because the diaphragm in its motion must reverse with the reversal of the current and the deflecting impulse if applied directly to the telephone receiver will be first in one direction and then in the other with a frequency so high that the diaphragm cannot follow or respond. Furthermore, if the diaphragm should respond with this frequency the effeet would not be audible. Also, in the case of the ordinary telephone, on account of the large self-inductance of the instrument, the high frequency E. M. F. enerated by the waves would produce in a telephone receiver only extremely weak currents. I have found it necessary, therefore, and consider it an important part of my invention to make use of some form of integrating detector to transform these rapid oscillations into effects which can be manifested by the indicating instrument.

In the drawings forming a part of this specification several modifications for the circuit connections are shown, and Figure 1 illustrates a form of circuit in which the high frequency oscillatory telephonic messages are impressed on the line by a bridge connection. Figs. '2 to .3 illustrate modifications of various. transmitting circuits. Figs. 6 to 9 illustrate various receiving circuits. Figs. 10 and 11 illustratemodifications of the connections shown in Fig. 1.

Referring to these figures in detail, Fig. 1 shows a common metallic circuit for ordinary telephony, across which are bridged the ordinary telephone sets 13 and B. These telephone sets include the usual apparatus as in present use in local battery telephone circuits. there. being shown a microphone transmitter l with its local battery 2 and the primary ot' the transformer -3. Also. there is shown connected in the usual way the ringing circuit 4 and the switchhook 5 with its receiver (3. The secondary of the transformer I; is bridged directly across the line wires A and A when the receiver is oil the hook. i

The invention is not in any way connected with the details of this telephone connection, any of the usual circuit connections being suitable, and the one described being given merely as an illustration.

Bridged across the line wires A and A at the same terminals or at any convenient distance from the terminals of the common battery telephone there is bridged a circuit containing a variable inductance L, variable capacity C, and the secondary S of a tran former. The primary P of the transformer is in circuit with a generator G of high frequency oscillations. and in circuit with the generator is also included a variable capacity C7,. and a suitable telephone transmitter, such as a microphone transmitter M. The transformer above mentioned is so con tructed as to be variable in its conplinggeither by sliding one coil within the other, varying the angle between the planes of the coils. or by any other suitable well ltnown arrangement. At the receiving end of the line there is bridged a similar circuit containing a variable inducance L and variable condenser and the primary P of a transformer. The secondary S of this transformer is connected in series with a variable inductance L and a variable condenser C". and around the condenser is shunted a detector D of the type commonly used in wireless tclegraphy. In circuit with the detector is connected, in the usual way. the telephone receiver, as shown at F.

The operation of the device is as follows:'

High frequency oscillations developed by the generator are impressed on the bridge circuit containing the inductance L and capacity C, which oscillations then travel along the line wires A and A and are received in the receiver R containing the oscillatory circuit 1." C". If these oscillations are modified in any suitable manner. an effect is iannediatcly produced in the receiver.

Vv'hile various means may be adopted to give the necessary variations to high frequency currents, l. have found it etl'ective and convenient to place in the circuit. of the generator, or .in the line itself. a microphone transmitter M. which produces no the sustained oscillations of high frequency slight modifications in amplitude of comparatively slow period. but corresponding in every detail with the ordinary voice vibrations. These modified oscillations when re ceivcd at R and transformed by the detector give. a reproduction in the telephone receiver F of speech transmitted from the generator circuit. Since these oscillations are of such high frequency they will produce no effect whatsoever in the batter)" sets ll and B", for the inqiedance, of these sets is so high forthese frequencies as to entirely prevent their passage. Fin-thermcre, any telephonic 9 currents transmitted by either of the sets P- and B will travel over the line wires a the same time as the high frequency cur rents. but they will in no way be influenced by. nor will they exert any sensible influence upon the high frequency currents. It has been found desirable in practice to tune the circuit comprising the line and bridgesto the frequency of the generator by means of the variable indnctances I. and L and the variable capacities C and C. The condensers C and C are also useful in preventing the passage of any telephonic currents from the sets B through the higa frequency bridge circuit, for these condensers are of exceedingly small capacity. being measured in thousandths of a microfarad. and thus interpose too large an impedance for currents of ordinary telephonic frequencie These condensers, however. when taken in connection with the inductances L and L. interpose a low impedance to the oscil-ations of such high frequencies as lie above 20.000 per second.

t nder certain conditions it may be desirableto have in series with the telephone sets B and B suitable inductance coils, which will beof such dimensions as to prevent the passage of the high frequency oscillations. but which ir.terpose only small impedance to the ord nary telephonic currents. In practice, however, this is found to be unnecessary, for the telephonee themselves contain sutiicient impedance for the purpose.

- Various forms of generator connections may be used as show 'mitter M and a variable primary P of a transformer. This circuit, as a whole, may be substituted, if desired, for the transmitter circuit shown in Fig. 1. For more carefully selected tuning, it is sometimes desirable to use the form of transmitter connection shown in Fig. 3, in which there is included a condenser C, and the variable inductance L,. In case the generator is limited in power, it is desirable to use the circuit shown in Fig. 3, hit-ring the same tuned to the frequency of the generator. In Fig. 4 there is shown still another form of generator circuit. In this casethe Duddellarc vissupplied with energy from the direct current generator G through the choke coils I. Around the are there is shunted an oscillatory circuit containing a. i'z'iriable capacity C, and a variable inductance L in series with the primary of a transformer P. This generator circuit may then be connected inductively to the bridge across the line wires, or. if desired, a weedingout circuit W ma." be interposed. This weeding-out circuit is well understood in the art, being made up of a variable condenser C in series with a variable inductance L and the necessary transformer coils as shown in F ig. 4. As shown in this figure, the telephonic variations in the oscillations may be introduced by means of a secondary circuit H containing a microphone or other suitable transmitter M and battery E and a primary of a transformer, said primary being inductively connectedto the inductance I1 T his inductive method of modifying the oscilla- Lions may be used inthe form of circuits shown in Figs. 1, 2, 3 and 5. In Fig. 5 still another form of generator of oscillations is shown, this generator consisting of a mercury v; or lamp connected in series with the D. generator G and suitable choke coils. the lamp being shunted by a capacity and inductance of an oscillatory circuit in the well known manner. Oscillations may.

then be modified by a microphone transmi ter M in any suitable manner as' described above.

In Figs. 6 to 9 there are shown modifications of the receiver circuit, and itis to be.

, able capacity C" and the secondary S of the transformer. This circuit is tuned to the frequency of the oscillations developed by the generator G. In shunt to the condenser is placed the detector D, which is of some the Perikon detector. Other well known" types are equally useful in this relation. In shunt to the detector is shown the telephone receiver F, with or without battery as may be desired. In Fig. 7 there is shown, in con nection with the detector circuit, a weedingout circuit W of a well known type. It is noted that in Fig. 7 the detector is connected directly in series with an oscillatory circuit containing the condenser C" and inductance L", this being a suitable connection only in case the detector is of a low resistance type. As shown in Fig. 8, it may not be necessary to have the detector circuit tuned when use is made of the weedin -out circuit W. Fig. 9 shows still another orm of receiver circuit, the oscillations being set up in a circuit containing the induuance L." and capacity-C". Around the condenser is shunted a detector D, such as the Perikon detector in series with a capacity K of fairly large electrzieal di' mensions. In shunt to the condenser K is the telephone receiver F.

Although numerous types of detectors have been used, I have. found the Audion an exceedingly useful type, for it requires very little attention in the way of adjustments. The connection of this Audion is shown clearly in Fig. 6, in which the exhaust bulb 11 contains the filament 12 and the electrode telephone receiver F and the battery 15.

Referring now to Fig. 10: It has been found possible to bridge across the line circuit A and A a plurality of high frequency circuits, each onesimilar in every respect to that described in Fig. 1. Preferably, the genenators differ from each other in frequency and differ. by such an amount-as to allow easy selective tuning. Itis apparent that these two high frequency oscillation enerators, shown in Fig. 10, will be entiredy independent of each other in the above properly tuned circuits, so that the oscillations, although existing together on the line, will be properly separated and selected at the receiving stations, that frequency generated at the transmitter T being selected by the receiver R. The local circuit: and each pair of bridge circuits with the line are tuned'to the same frequencyiand to the frequency of the generator T. Also the receiver R is tuned to the same frequency as the generator T. It is obvious, in connection with this, that telegraphic messages may be transmitted as well as telephonic messages. This is illustrated in the transmitter at T, in which the microphone transmitter is replaced by the interrupter N and the telegraphic key 17, this key being shown in detail in Fig. 3. In said Fig. 3 there. is shown the key K, around which is shunted a varireceivers at each end.

able portion of this element 0 is shunted by the interrupter N. This avoids the necessity of completely breaking the generator current, and the signals are made merely by modifying the oscillations with a definite frequency. Obviously, many modifications ofthis key may be used. This form of telegraph transmitter may obviously be substituted for any of the telephone transmitters. By means of this system it is possible to transmit simultaneously the ordinary telephonic speech by means of the sets 13 and B and high frequency telephonic messages by means of the transmitter T, and also tel eyraphic messages by means of the transn.itter T.

In Fig. 11 there is shown a still further modification. in which a plurality of transmitters and receivers are bridged across the line. In this Fig. 11 the generator circuits "1' are indicated only diagrammatically by the coil of wire, it being understood that this represents any of the transmitters shown in Figs. :2 to 5. The receivers are shown at R and only diagranunatically, it being understood that. any of the receivers shown in Figs.- 6 to 9 being useful in this connection. Obviously, it is possible and desirable to have some of these transmitters at; one end of the line and the others at the other end. as indicated by the reference letters T and R. The receivers may be placed some at one end and some at the other, and in prac tice it would ordinarily be convenient to have the'same number of transmitters and It is of course under- 1 ood that each transmitter has a frequency of its own. and that one receiver and its bridging circuit with the line are tuned to the frequency corresponding to their transmitter. All of these high frequency currents may exist upon the line simultaneou. and have no perceptible elt'ect upon ea" whatsoever upon the ordinary battery t phonic currents transmitted in the 1151 way. In Figs 10 and 11 the telephone sets B are merely indicated, it being understood that such a set as is shown in Fig. l is to be used. It may be desirable in certain cases to omit the ordinary battery telephonic sets entirely, in which case the multiplex telephony would be carried on entirely by high frequency currents of different periods.

In case a common battery telephone circuit is used, instead of local battery sets as shown. it will be 116088. y to shunt the repcatinp coils by variab c condensers 0:. such small capacity as to offer a high im dance to ordinary telephone currents but ow im- 1 system,

inductaiices, it will be necessary to put in similar shuntcondensers.

'l. he generators here described have a single period, but it is obvious that use may be made of multiperiod generators, in which case the individual frequencies from said generators would be used in separate transmitter circuits.

Although several modifications have been described in detail in this specification, it is obvious that many other changes may be made Without departing from. the spirit of the invention, and I therefore do not Wl-Sl'l to be limited to the exact connections shown, but

That I claim as my invention is the following:

1. In a multiple: telephone and tel raph system, the combination of a pair of line wires, battery telephone sets oridged across said. line wires; means at one end for impressing high frequency oscillations on said line wires; means for modifying said oscilla- =r-ions in accordance with speech; means at the other end for detecting said oscillations the complete circuit for the high frequency oscillations being tuned to the frequency of the oscillations.

9 In a multiplex telephone and tele in h system, the combination of a )air 0 line wires, battery telephone sets bridged across said line wires; a generator of frequency electric waves or oscillations inductively connected to said line wires, means for modifying the oscillations; a receiver circuit inductively connected to the line wires and tuned to the f uency of the generator, an integrating iiet rtor'in said receiver circuit and a telephone operatively connect-ed thereto.

3. In a multiplex telephone and tele the combination of a raph pair of line u res, a plurality of generators of high fre- "i i quency oscillations inductively connected to I sa d line wires. means in each generator cirother. nor will they have anv sensible efi'r ct i suit for niocii g the oscilla e i; a plucircuits indric ively con- Wires. each recesver circuit being tuned l he frequency of one of the generators, an integrating detector in each receiver circuit and a telephone operatively connected to each detector.

4. In a multiplex telephone and telegraph system. the combination of a pair 0 line wires, battery telephone sets bridged across a generator of high frequency oscillations, a signaling instrument for modifying the high frequency oscillations, said generator being inductively conn uteri to a circuit bridged across the line wires at one end thereof, a simiar circuit bridged across the circuit, at the other end and a receiver circuit inductively connected pedance to the high frequency oscillations. thereto said bridges with the line Wires be- Also, in case of loading coils or other high 1 ing tuned to the frequency of the generator.

8 asciszse ceiver circuit inductively connected to said, "last named bridge circuit, said bridge circuits with line wires being tuned to the frequency of the generator.

6. In a multiplex telephone system, he combination of a air of line wires, batter, telephone sets bri ged across said line wires, a generator of high frequency oscillations. a microphone transmitter for modifying the high frequency oscillations, said generator being inductively connected to a circuit bridged across the line wires at one end thereof, said bridging circuit comprising a condenser and an inductance in series with the secondary of a transformer; a similar circuit bridged across the line at the other end and a receiver circuit inductivelv connected thereto, said bridge circuits with line wires being tuned to the frequency of the generator.

7. In a multiplex telephone system, the combination of a pair of line wires. a battery telephone set bridged across said line wires at each end thereof, a generator of high frequency oscillations, a micro hone transmitter for modifying the big frequency oscillations, said generator being inductivelv connected to acircuit bridged across the line wires at oneend thereof, said bridging circuit comprising a condenser and an inductance in series with the secondary of a transformer; a similar circuit bridged across the line at the other end and a receiver circuit inductively connected thereto, said receiver circuit being tuned by means of a capacitv and inductance to the frequency of the gerierator and said receiver circuit including a detector of high frequency oscillations, and a telephone receiver operatively connected to said detector.

8. In a multiplex telephone and telegraph system, the combination of a pair of line wires, battery telephone sets bridged across said line wires. a plurality of circuits bridged across the line wires, each circuit including a variable capacity and induc tance; a plurality of sources of high frequency oscillations, one inductively connected to each of the bridge circuits. a signaling instrument in circuit with each source of oscillations to modify the said oscillations, a plurality of similar circuits bridged across the line and a plurality of receiver circuits, one inductively connected to each of the bridge circuits, each receiver cir' cult and each pair of bridge circuits "with the line wires being tuned to the frequency of the corresponding generaton.

9. In a multiplex telephone system, the combination of a pair of line wires, a battery tel phone set bridged across said line wires at each end thereof, a plurality of-circuits bridged across the line wires, each circuit includin a variable capacit and inductance; a gurality of sources 0 high fre qucncy oscil ations, one inductively connected to each of the bridge circuits, a signaling instrument in circuit with each source of oscillations to modii' the said oscillations, a plurality of simi ar circuits bridged across the line and a plurality of receiver circuits, one inductively connected to each of the bridge circuits, each pair 'ofbridge circuits with the line and the corresponding receiver circuit being tuned to the frequency of one of the transmitter circuits, each receiver circuit containing a detector of high frequency oscillations and having a telephone receiver operatively connected thereto.

10. In-a multiplex telephone system, the combination of a pair of line wires, a plurality of circuits bridged across the line wires, each circuit including a variable capacity and inductance for tuning, a plurality of sources o'fdiigh frequency OSClllt'l: tions, one inductively connected to each of the bridge circuits, a signaling instrument in circuit with each source of oscillations to modify the said oscillations, a plurality of similar circuits bridged across the line and a plurality of receiver circuits, one inductively connected to each of the bridge circuits, each pair of bridge circuits with the line and the corresponding receiver circuit being tuned to the frequency of one of the transmitter circuits, each receiver circuit containing a detector of high frequency oscillations and havin a telephone receiver operatively connecte thereto. r

11. In a multiplex telephone system, the combination of a pairof line wires, battery telephone sets bridged across said line wires, a plurality of local transmitter circuits, each circuit including a high frequency dynamo in series with a variable capacity, a variable inductance, a signaling instrument and the primary of a transformer; a plurality of local receiver circuits, comprising a variable condens r in series with a variable inductance and the secondary of a transformer coil; a vacuum detector shunted around said condenser and a telephone head-piece operativelv connected to said vacuum detector; a plurality of bridging circuits connected across the line wires, each circuit containing a variable capacity and a variable inductance for tuning; a bridging circuitinductively cemiected to each transmitter cir-' emit; a bridging circuit inductively connected taeach receiver circuit, each pair of bridging circuits with the line and its corre- 5 spending receiver circuit being tuned to the frequency of the can-es nding transmitter circuit, said plurality oi transmitter stations I thehue wire.

' GEORGE OWEN SQUIER.

Witnesses:

- P. I. Wow,

E. R. Gum.

and receiver stations being distributed along 

